As shown in FIG. 28, in an architecture of LTE (Long Term Evolution), eNBs 601 to 604, which are RAN nodes, are connected to an MME (Mobility Management Entity) 610 and an S-GW (Serving Gateway) 620, which are nodes belonging to a core network. When incoming data is transmitted to UE (User Equipment) in an idle state, for example, a sequence as shown in FIG. 29 is conducted. Specifically, when the MME 610 receives a Downlink Data Notification from the S-GW 620, it transmits a paging message to the eNBs 601 to 604. At this time, the MME 610 transmits Paging to the eNB located in an area where the UE has newly registered its location.
Here, the area where the UE has registered its location is represented by a TA (Tracking Area). The TA is an identifier (ID) indicating a logical location, and an operator can freely decide a size of an area covered by the TA according to a region and a traffic condition. Generally, if an area covered by one TA is large, the number of eNBs under control of the TA also tends to increase. In addition, even though the UE at idle time moves between the eNBs belonging to the same TA, location registration is unnecessary. That is, the number of signals concerning location registration generated in the UE moving between the eNBs can be suppressed by increasing the area covered by the TA.
To summarize, when an incoming call to the UE is generated, the MME transmits the paging message to an area covered by a newest TA where the UE is located.
Although FIG. 29 shows four eNBs as an example for simplicity of explanation, generally, for example, from hundreds of to one thousand eNBs may be present in the area covered by the TA. In such a case, the MME transmits the paging message to all the eNBs. Namely, the MME must transmit the paging message to from hundreds of to one thousand eNBs within an extremely short time. As a result, a load on processing of the paging message of the MME rapidly increases.
Non Patent Literature 1 discloses a proposal on paging optimization in which when one or more certain appropriate eNBs receive a paging message from an MME, and the eNBs that have received the paging message transmit the paging message to neighbouring eNBs instead of the MME in order to reduce a processing load in the MME. The proposal according to Non Patent Literature 1 has been discussed in 3GPP (3rd Generation Partnership Project). This example is shown in FIG. 30.
FIG. 30 shows that when the eNB 601 receives the paging message from the MME, it transmits the paging message to the neighbouring eNBs 602 to 604 instead of the MME 610.